Two-dimensional numerical simulations of ablatively accelerated thin-shells subject to Rayleigh-Taylor instability are presented. Results for both single wavelength and multiwavelength perturbations show that the nonlinear effects of the instability are evident mainly in the "bubble" rather than the "spike." Approximate roles for predicting the dominant nonlinear mode-mode interactions, which limit shell performance, are also discussed. The work concludes with a discussion of recommendations for future work in this area.

A transient code (TFETC) for calculating the temperature distribution throughout the radial and axial positions of a thermionic fuel element (TFE) has been successfully developed. It accommodates the variations of temperatures, thermal power, electrical power, voltage, and current density throughout the TFE as a function of time as well as the variations of heat fluxes arising from radiation, conduction, electron cooling, and collector heating. The thermionic fuel element transient code (TFETC) is designed to calculate all the above variables for three different cases namely: 1) Start-up; 2) Loss of flow accident; and 3) Shut down. The results show that this design is suitable for space applications and does not show any deficiency in the performance. It enhances the safety factor in the case of a loss of flow accident (LOFA). In LOFA, it has been found that if the mass flow rate decreases exponentially by a -0.033t, where t is a reactor transient time in seconds, the fuel temperature does not exceed the melting point right after the complete pump failures but rather allows some time, about 34 seconds, before taking an action. If the reactor is not shut down within 34 seconds, the fuel temperature may keep increasing until the melting point of the fuel is attained. On the other hand, the coolant temperature attains its boiling point, 1057 ��K, in the case of a complete pump failure and may exceed it unless a proper action to trip the reactor is taken. For 1/2, 1/3, and 1/4 pump failures, the coolant temperatures are below the boiling point of the coolant. / Graduation date: 1994

Thesis--University of Illinois at Urbana-Champaign, 1977. / Includes bibliographical references (p. 126-128).

The steady flow model is applied to ablatively accelerated spherical targets for inertial confinement fusion. A parameter study is conducted which identifies regions of good hydrodynamic efficiency. In the limit of very large acceleration the model is seen to become planar and can be used to treat some large aspect ratio shells. A model of charged particle beam driven ablation is presented. The ablation resulting from this form of energy deposition can resemble laser driven albation in some cases, but qualitatively different behavior occurs in certain regimes of the beam power and range. Laser energy deposition by inverse bremsstrahlung is also included. A procedure for descaling the dimensionless results of the steady flow model is presented. This allows for comparison of the model with experiments and numerical simulations.